Federal health officials have directed airlines to provide the Centers for Disease Control and Prevention with the names and contact information of all passengers who boarded flights bound for the United States since Nov. 29 and who had been in southern Africa during the prior two weeks.The directive, issued Wednesday, applies to passengers who spent time in Botswana, the Kingdoms of Eswatini and Lesotho, Malawi, Mozambique, Namibia and South Africa in the two weeks before flying to the United States. The airlines were directed to provide their names, addresses while in the United States, phone numbers, email addresses, dates of birth and flight information, including seat numbers.“C.D.C. is issuing this directive to prevent the importation and spread of a communicable disease of public health importance,” a statement from the agency said, an apparent reference to the new Omicron variant of the virus that causes Covid.Last week, the White House announced a ban on travel from eight countries in southern Africa. And late Tuesday night, the C.D.C. said it planned to toughen virus testing and screening of people flying to the United States by requiring all international passengers to provide a negative result from a test taken within 24 hours of departure.The new directive was issued under an Oct. 25 order that instructed airlines and aircraft operators to collect specific information from all passengers before boarding, retain the information for 30 days, and transmit it to C.D.C. within 24 hours if requested to do so.The C.D.C. can share the information with state and local health departments at passengers’ destinations, enabling local health authorities to monitor travelers for Covid, identify symptomatic individuals, notify their contacts, and direct those who are infected to isolate and their contacts to quarantine to avoid further disease spread. They can also use the information to ensure infected individuals get appropriate care.The order applies to flights that have departed for the United States since Monday morning. Two flights left Johannesburg for the United States that day: a Delta Air Lines flight with more than 300 seats that was headed for Atlanta, and a United Airlines flight with more than 250 seats that was headed for Newark, N.J. Both flights landed in the United States on Tuesday morning, according to schedules from Cirium, an aviation data provider. Two more United flights are scheduled to leave South Africa for Newark on Wednesday, one from Cape Town and one from Johannesburg.Delta and United are currently the only two carriers that offer direct or single-layover flights between the countries covered by the C.D.C. order and the United States, according to Cirium schedule data. Delta operates three weekly flights between Johannesburg and Atlanta. United operates five flights a week between Johannesburg and Newark. It also plans to restart seasonal flights between Cape Town and Newark on Wednesday.Both airlines have said that they are not planning to adjust their flight schedules in response to the administration’s ban on travelers from the region, which took effect on Monday and does not apply to American citizens or lawful permanent residents. The airlines also said that they plan to comply with the C.D.C. order.Sixty-one people who arrived in the Netherlands on Friday aboard two flights that departed from South Africa tested positive for the virus that causes Covid, including over a dozen who were carrying the new Omicron variant. The number of overall positive cases represented more than 10 percent of the 600 passengers tested.